"Waterless " cooking is old, as are knobs which give an audible signal when steam is formed to indicate attainment of cooking temperatures. For instance U.S. Pat. No. 999,567; 957,663; and 875,310 all show tops for cooking vessels which are provided with whistles and the first two have provision to turn the whistle off, in the case of U.S. Pat. No. 957,663 also stopping the escape of steam. However, mechanically these are quite different from my device. The only one which can be disassembled for cleaning could also release the knob portion accidentally under steam pressure, which might well cause loss of the knob or even injury. The remainder of these patents and U.S. Pat. No. 700,864 cannot be disassembled for cleaning.
None of these structures involve a slide valve. Slide valves are of course known in other connections but a slide valve possesses unique advantages in a whistle knob not apparent from the known prior patents. Likewise, the method of assembly is believed to possess unique advantages.